Inflow & Infiltration

Inflow:
Inflow is stormwater that enters the wastewater network directly through gully traps, roofs or illegal connections.  Common sources of inflow include roof downspouts, leaking manholes, cross connected storm drains, cellar drains, yard/foundation drains and sump pumps.

Infiltration:
Infiltration is stormwater or groundwater that enters the wastewater network through cracked pipes.

Why is I/I an issue?
Reducing I/I improves operational efficiencies by reducing the amount of flow that enters the wastewater pipes improving sewer network capacity and reducing the amount of flow that needs to be treated at the Treatment Plant.  Reducing I/I also leads to less combined sewer overflow situations where too much stormwater is introduced into the wastewater system and the system overflows directly into the Presumpscot River.

Inflow and Infiltration

Flow Metering

Flow metering is used to perform inflow and infiltration analysis within a wastewater system.  It is done using flow meters, rain gauges and groundwater gauges and helps investigate extraneous flow in the wastewater collection system.  The ultimate goal of flow metering is to reduce the cost associated with conveying I/I to the Wastewater Treatment Plant, increase the capacity within the system, and reduce the occurrence of combined sewer overflows.  With the flow metering data, we can determine which areas in the City have the most inflow and/or infiltration and where we can perform a sanitary sewer evaluation survey (SSES).